The present invention relates to a system and method for reducing speed of a vehicle.
xe2x80x9cAutomatic distance regulationxe2x80x9d (ADR) systems have been proposed that are intended to detect and carry out a controlled braking action to control the distance of a vehicle from other vehicles and/or stationary objects in the direction of vehicle motion. JP-A 7-144588 discloses a system whereby traveling speed and deceleration of a vehicle in front are determined using a Doppler sensor and a vehicle speed sensor, which are on a vehicle to be controlled, and a desired distance from the vehicle in front is determined in response comparison of the traveling speed of the vehicle in front with a predetermined value of 15 km/h. In this system, a driver is warned and an automatic braking action is initiated if the distance from the vehicle in front becomes less than the desired distance. JP-A 10-114237 discloses a technique to release ADR in response to operator demand for acceleration to pass a vehicle in front without relying on detection of accelerator pedal position. A throttle of an engine is coupled with a throttle actuator and an accelerator pedal. A sensor is provided to detect an actual throttle position. Using a predetermined characteristic curve, a throttle position is estimated from a present position of the throttle actuator. The operator demand for acceleration is detected after comparison of a deviation of the actual throttle position from the estimated throttle position with a threshold value. The deviation is zero when the accelerator is released, but the deviation exceeds the threshold when the accelerator pedal is depressed.
Other systems have been proposed that are intended to initiate braking action before the operator of a vehicle initiates braking action. JP-A 6-24302 discloses a system whereby, when a foot of the operator leaves an accelerator pedal, two micro switches are both closed to energize a solenoid for activating a brake pedal. Energizing the solenoid pulls the brake pedal to partially activate a braking system before the foot of the operator is stepped on the brake pedal.
Commonly assigned co-pending U.S. patent application Ser. No. 09/640,792 filed on Aug. 18, 2000 discloses a preview brake control system for assisting vehicle operator braking action. For assisting vehicle operator braking action, a detection sub-system on a vehicle to be controlled detects obstacles, which are in or near the direction of motion of the vehicle, and provides corresponding environmental data to a brake controller. In addition, the vehicle has vehicle condition sensors for detecting parameters indicative of the condition or state of motion of the vehicle and transmitting corresponding data to the controller, and vehicle operator demand sensors for detecting parameters indicative of power or brake demand of the operator and transmitting corresponding data to the controller. From the data reported concerning the obstacles, the vehicle condition parameters and the operator demand parameters, the controller ascertains whether or not there is a need for operator braking action. The controller determines a stand-by braking torque in terms of a brake pressure and generates a braking signal for a braking sub-system or braking device to apply the stand-by braking torque to at least one or wheels of the vehicle. As sensors for detection of the obstacles located in or near the direction of motion of the vehicle, conventional radar sensors employing laser, whose application is familiar to those skilled in the art, are used. However, any other types of sensors that permit an adequate preview of the range of motion of the vehicle and which are suitable for service under rough vehicle condition may be used. For full description of the preview brake control system, U.S. patent application Ser. No, 09/640,792, which has its corresponding European Patent Application No. 00307108.1 filed on Aug. 18, 2000, has been hereby incorporated by reference in its entirety.
If the preview braking system is installed in a vehicle having an ADR system, there is little possibility that the preview braking system generates a braking signal for a braking device to apply a stand-by braking toque to at least one wheel of the vehicle while the ADR system in operation. However, there is certain situation where the ADR system generates an ADR braking torque request representing an ADR braking torque to maintain a set desired distance from a preceding vehicle simultaneously with generation of a braking signal by the preview brake control system. This situation appears if the vehicle operator turns on an ADR switch to initiate operation of ADR system when the preview brake control system generates a braking signal for the braking device to apply the determined stand-by braking torque to the at least one wheel. If the ADR braking torque is less than the stand-by braking torque when the ADR system is put into operation, a transition from the stand-by braking torque to the ADR braking torque gives an interruption to deceleration. This transition between braking modes may be noticeable to the operator.
It is an object of the present invention to provide a system and method for reducing speed of a vehicle using transition braking torque to provide smooth and consistent transition from application of braking torque by preview brake control system to application of braking torque by automatic distance regulation (ADR) system.
In carrying out the above object and other objects, advantages, and features of the present invention, a system for reducing speed of a vehicle, comprises a braking device coupled to at least one wheel of the vehicle for applying a braking torque to the at least one wheel in response to a braking signal, and a controller having a control logic for determining whether or not there is a need for operator braking action, determining a stand-by braking torque when there is a need for operator braking action, determining a transition braking torque based on the stand-by braking torque and an automatic distance regulation (ADR) braking torque, and generating a braking signal for the braking device to apply the transition braking torque to at least one wheel of the vehicle. The ADR braking torque is represented by an ADR braking torque request that is generated when an actual distance from a preceding vehicle becomes less than a set desired distance. In one embodiment, the transition braking torque is determined by holding the transition braking torque as high as the stand-by braking torque for a predetermined period of time since the determination was made that there was a need for operator braking action, comparing the stand-by braking toque to the ADR braking torque upon elapse of the predetermined period of time, and holding the transition braking torque as high as the stand-by braking torque over extended period of time after elapse of the predetermined period of time when said ADR braking torque is less than the stand-by braking torque upon elapse of the predetermined period of time.
In carrying out the present invention, a method for reducing speed of a vehicle comprises determining whether or not there is a need for operator braking action, determining a stand-by braking torque when there is a need for operator braking action, determining a transition braking torque based on the stand-by braking torque and an automatic distance regulation (ADR) braking torque, and applying the transition braking torque to at least one wheel of the vehicle.
In carrying out the present invention, a computer readable storage medium is provided, which has stored data representing instructions readable by a computer to reduce speed of a vehicle. The computer readable storage medium comprises instructions for determining whether or not there is a need for operator braking action, instructions for determining a stand-by braking torque when there is a need for operator braking action, instructions for determining a transition braking torque based on the stand-by braking torque and an automatic distance regulation (ADR) braking torque, and instructions for applying the transition braking torque to at least one wheel of the vehicle.